The present invention relates to apparatus for severing fibrous material, especially for severing cables or tows consisting of textile filaments.
Many branches of textile industry utilize relatively short fragments of filamentary material which are obtained by severing a continuous tow or cable of filaments at regular intervals. The length of fragments of filamentary material depends on their intended use and normally varies between a few millimeters and two hundred millimeters. As a rule, the tow which is to be severed to yield fragments of filamentary material having a predetermined length consists of crimped fibers. At the present time, the requirements for fragments of crimped filaments greatly exceed the demand for uncrimped fibers. The severing operation is preferably carried out while the filaments are under tension so that the crimp disappears during severing; this insures that the filaments can be subdivided into fragments of identical length. The crimp reappears as soon as the filaments are severed, i.e., immediately upon termination of the tensional stress. In order to insure an economical operation, the tow of filamentary material must be fed to the severing apparatus at an elevated speed, preferably in excess of 300 meters per minute.
In a presently known severing apparatus, the tow is caused to pass between two rubber-coated rollers having radial slots for knives which move radially outwardly when in register with the nip of the rollers to thereby sever the filaments of the tow. Such apparatus operate satisfactorily, even when the tow is fed at a high speed. However, the wear on their parts is high and the mechanism for moving the knives radially of the rollers is complex and prone to malfunction.
It is also known to utilize severing apparatus wherein the tow is convoluted onto a rotary drum having rigid radially outwardly extending knives. The cutting edges are located at the radially outermost ends of the knives. An elastic roller cooperates with the drum to urge the tow against the cutting edges of successive knives whereby the tow yields fragments in response to severing of the innermost convolution or winding of the tow. The fragments are evacuated by suction through the interior of the rotating drum. The path along which the fragments of severed filaments are evacuated includes the spaces between neighboring knives of the drum; the width of such spaces decreases in a direction toward the axis of the drum so that the fragments are likely to accumulate into bunches which clog the spaces and are unable to enter the interior of the drum. The tendency of fragments to form accumulations or bunches of interlaced fibrous particles is further enhanced by the fact that the filaments of the tow are normally twisted. Another drawback of the just described apparatus is that the stretch of filaments which form convolutions around the periphery of the drum decreases in a direction toward the axis of the drum, i.e., the tensional stress upon the filaments which are being severed by the cutting edges of the knives is considerably less than the tensional stress upon the filaments which form the outermost convolution of the tow around the periphery of the drum. This reduces the reproducibility of the severing operation because at least some of the filaments exhibit a pronounced crimp at the time they are being severed by the knives.